1. Field of the Invention
This invention relates generally to a method and apparatus for varying the output from two hydraulic power sources, and more particularly to such methods and apparatus as used to steer prime movers such as crawler tractors.
2. The Prior Art
Various types of mechanisms have been used in the prior art to regulate the power output from a pair of tandem hydraulic swash-plate type pumps supplying fluid motors driving an actuated device or vehicle. Most typically, a pair of independent hand-operated speed control levers have been used to enable steering, such as shown for example in U.S. Pat. No. 3,898,811, incorporated by reference. Other mechanisms have included a single hand-operated lever and two foot-operated steering pedals, but have also included complex hydraulics interconnected with the foot-operated pedals. These hydraulic systems have been relatively expensive and have required frequent maintenance.
Thus, a relatively inexpensive, trouble-free mechanism for use with a single operator lever and a pair of foot operated steering pedals has not been available.